PC not booting into OS

Ok so here is the deal. I woke up and found that my OS had crashed. So I replaced Vista and installed XP. I fooled around on XP to find out what was still there and of course all my files were gone. I thought by chance some of the files would be there because the install was not a format. At any rate the files on the other internal hard drives were there.

So I then upgraded my XP to Win 7. I had got everything working on Win 7, then my wife asked me to go to the store. I left the pc on as I was just about to install Office. When I returned home my keyboard and mice would not respond. So I restarted the computer. It came on fine. I installed Microsoft Security Ess. I got to the part where I had to restart the computer.

Then the computer wont boot into the OS. I tried restarting again and again and it still would not boot into the OS. It just stays at the start up screen which shows that I have an XFX motherboard. I turned the power completely off for 15 mintues to try and again and nothing.

I since have left for 48 hours and have not tried turning it back on yet. I plan on trying it again after work but I wanted to come here for Ideas first. I just dont know if its the HD just yet. Its a 150gig harddrive isolated only to my OS and programs. All my other media for music and videos for ITunes/ Mediamonkey is stored on another internal HD.